Creates a new handle and opens a connection to the kernel sequencer
interface. After a client is created successfully,
a ClientStart event is broadcast to the announce port.
May throw an exception.
See also: open_lconf, close, get_seq_type,
get_seq_name, set_blocking, get_client_id.

Close the sequencer. Closes the sequencer client and releases its
resources. After a client is closed, an event with ClientExit is
broadcast to announce port. The connection between other clients are
disconnected. Call this just before exiting your program.
NOTE: we could put this in a finalizer for the handle?

Change the blocking mode of the given client.
In block mode, the client falls into sleep when it fills the output
pool with events, or when it demands events from an empty input pool.
memory pool with full events. Clients that are sleeping due to
loack of space in the output pool are woken when a certain
amount of free space becomes available (see set_output_room).